When two or more people sign a lease or rental agreement together, they become co-tenants and share the same legal rights and responsibilities. Many leases contain language stating something to the effect of "tenants are jointly and severally liable for paying rent and adhering to the terms of the agreement."

This means that each roommate is independently responsible for the entire rent – not just a portion of the payment.

In other words, if one roommate doesn’t contribute to the rent payment, the other roommate(s) are still on the hook for the entire payment. A landlord has the legal right to hold all co-tenants responsible for the negative actions of one and can evict all the tenants even if only one violated the lease or rental agreement.

If just one roommate originally rented the property, that roommate would be completely responsible for the rent, including for collecting rental shares from other roommate(s). In that case, a roommate agreement is especially important. Check the lease in advance to make sure that the landlord doesn't require each tenant in the unit to sign the lease or have other regulations about sharing or subletting the space (see below).

Lease

Most landlords require tenants to sign a written lease – a conveyance of a possessory estate in real property and a contract between the landlord and tenant. There are three different types of residential leases that express various terms for the rental agreement: tenancy for years, tenancy from period to period and tenancy at will. Each lease identifies a starting date for the tenancy and, depending on the type of lease, an end date. A fourth type of lease – a tenancy at sufferance – is never intentionally entered into (lease types are covered in more detail in the Tenants, Landlords and Types of Leases section of this tutorial).

If you want to add a roommate to your lease or rental agreement, your landlord will probably perform the usual credit and reference checks for any additional tenants and ask all tenants to sign a new lease or rental agreement. Because tenants are "jointly and severally liable" for paying the rent and any damages, the landlord benefits from including all tenants on a new lease. The new lease also makes it clear to all tenants that each shares the same legal rights and responsibilities.

Adding a roommate to a lease might result in a rent increase, presumably to cover the additional wear and tear on the unit. The new lease signifies a new tenancy, so the landlord can increase the rent immediately (instead of giving any notice or waiting until the lease ends). The landlord also has a legal right to increase the security deposit on the unit: The amount of the security deposit is typically based on the rent, so if the rent increases, the landlord can raise the security deposit correspondingly. (For related reading, see Do Landlords Set Up Escrow Accounts for Their Tenants’ Security Deposits?)

Finding a Roommate

If you decide to find a roommate (for financial and/or social reasons), it makes sense to find someone who has similar housing goals – whether that’s a quiet home life, loud music and parties, or something in between. Regardless of lifestyle, it’s important that all roommates share common goals; otherwise, the living situation can quickly turn bad. (For more, see How a Bad Roommate Can Ruin Your Credit Score.)

You can find a roommate by word of mouth, Craigslist, campus newspapers or by using an online roommate-matching service such as Roommates.com and RoomieMatch.com. It may be easier to find a compatible roommate if you ask some questions: When should music be turned off? How will cooking and food shopping be delegated? Who will write the checks for rent and utilities? Is it okay for friends to spend the night and, if so, how often? How will rent be divided? Who will get which bedroom?

It’s also appropriate to ask where the rent money will come from. Is the potential roommate employed? If the person is a student, are his or her parents helping with rent and expenses?

Determining "exit procedures" is also helpful. How much notice will you give one another before moving out? How long will a roommate continue to pay rent if they move out? Will they be responsible for finding a replacement?

Starting a conversation ahead of time can help create a better experience for everyone. For added peace of mind, you might consider signing a "Roommate Agreement" that defines the terms of the co-tenancy and outlines details such as each person's share of the rent and utilities, who gets which bedroom, how will chores be divided, how food and shopping will be handled, rules regarding guests and plans for dispute resolution. (For more, see 5 Tips for First-Time Renters.)

Sharing the Rent

You can divide the rent equally amongst the co-tenants or determine some other percentage for each person. It’s not uncommon, for example, for the room with the largest bedroom and private bathroom to pay a higher share of the rent. Similarly, if one tenant takes up more space in the property – perhaps by commandeering the office space or the garage– he or she will likely be responsible for a greater share of the rent. The landlord's only concern is that the total rent is paid on time each month. The co-tenants are free to divide the rent as they see fit.

At times, roommates may find it’s appropriate to divide the utilities based on usage. One roommate, for example, may not watch TV. The roommates may decide that person won’t have to contribute to the cable bill. Likewise, one tenant might use much more electricity than the average person (for example, they have to keep their window AC unit running all the time because of allergies). That person might chip in a little more each month to reflect the extra usage. You can avoid household disagreements by deciding ahead of time how to handle the rent and utilities – use an app like Splitwise or IOU to help you keep track of bills and payments.

Sharing Chores

Even though the landlord is responsible for the majority of maintenance inside the unit and the common areas, the tenants are still in charge of normal household chores such as cleaning the bathrooms, vacuuming/sweeping/mopping the floors, cleaning the kitchen, and taking out the garbage and recycling. Without a schedule, it’s easy for one roommate to end up doing the majority of chores. It’s a good idea to create a list of daily, weekly and monthly chores, and identify who will complete each task – and when they’ll do it. Using an app like Tody or Wunderlist can make it easy.